The color negative-positive photographic system relies on the exposure of a scene onto a color negative film. The exposed negative is then projected onto a negative-working color photographic paper to form, after development, the desired positive image. In order to correctly expose the photographic paper, the average density of the negative in all three color records (red, green and blue) must be measured so that the exposure time and balance between the amounts of the R, G and B light used to expose the paper can be adjusted.
The general practice in the photofinishing industry is to read the average color density of the negative using red, green and blue filters. There is no uniform standard for these filters. Different sets of filters may read the same negative differently because of variations in the amount of light they pass. In most cases, this is not a problem since the response of a printer filter set is accounted for in the calculation for the subsequent exposure of the paper. However, this method assumes that the measured red, green and blue densities of any and all negatives to be printed by a particular printer system reflects the color balance of the original scene.
Pyrazolotriazoles have been used as magenta couplers in commercially available color negative films and can offer useful photographic advantages such as high coupling efficiency, formaldehyde insensitivity and low unwanted absorbance, even though they have high pH sensitivity and complicated syntheses. The hues of the magenta dyes formed from pyrazolotriazoles are broad in terms of bandwidth, with substantial density at wavelengths from 565 to 600 nm. Four-equivalent 1-phenyl-3-acylamino-5-pyrazolones are also used as magenta couplers in commercially available color negative films and can offer useful photographic advantages, even though they suffer from low coupling efficiency and sensitivity to formaldehyde. The hues of the magenta dyes formed from 1-phenyl-3-acylamino-5-pyrazolones are broad in terms of bandwidth, with substantial density at wavelengths from 560 to 590 nm, similar to pyrazolotriazole based dyes.
1-Phenyl-3-anilino-5-pyrazolones are also used as magenta couplers in commercially available color negative films and can offer useful photographic advantages such as low pH sensitivity, high coupling efficiency and ease of synthesis. However, the hues of the magenta dyes formed from 1-phenyl-3-anilino-5-pyrazolones are associated with narrower bandwidths than those formed from pyrazolotriazoles or 1-phenyl-3-acylamino-5-pyrazolones, with much less density at wavelengths from 565 to 600 nm. Although the foregoing numbers may vary depending on the particular color developer used, for most color developers they will be within a few nanometers. In the present application, all of the wavelength measurements given are with reference to development of the element with 2-[(4-amino-3-methyl phenyl)ethylamino]ethanol, as typically used in the industry for development of negative films as in KODAK FLEXICOLOR II Process (British Journal of Photography Annual, 1988, pp 196-198).
Thus, negative films using each of the above types of magenta couplers can be prepared so that the red, green (measured at one wavelength, i.e. 550 nm) and blue densities are matched. Because photographic paper has a narrow peak sensitivity range of 545-555 nm and low sensitivity at greater than 565 nm, films containing any of the aforementioned magenta image couplers would appear equivalent to the paper. However, the film with the 1-phenyl-3-anilino-5-pyrazolone magenta coupler would have less density in the region of 565 to 600 nm than the others. Printers whose green filters do not significantly read densities at wavelengths greater than 565 nm would record all three films as having the same green density. Printers with green filters that read density at wavelengths longer than 565 nm, however, would measure the film containing a 1-phenyl-3-anilino-5-pyrazolone as having less green density than the others. Since the red and blue density determination by the printer are relatively independent of the magenta coupler, such a printer would not give the film containing the 1-phenyl-3-anilino-5-pyrazolone the same exposure as the films with the other magenta couplers. Thus, paper images printed from a film containing 1-phenyl-3-anilino-5-pyrazolone magenta coupler would not have the same color balance on this type of printer as films containing either of the other two types of magenta couplers. For example, commercially used printers such as KODAK Printer Models 2610 or 3510 have green filters that do not read significant amounts of density at greater than 565 nm and so are not as sensitive to magenta dye absorption differences in the 565-600 nm range. However, other commercially available printers such as the KODAK Class 35 Printer, AGFA MSP Printer or the NORITSU 1001 Minilab have green filters that will read films with these different classes of couplers as different in overall green density.
In order to get color prints with matched color balance from films containing each of these three magenta couplers when printed using printers that read significant amounts of density from 565 to 600 nm, photofinishers must either segregate the different films so that the correct calculation of the exposure for that particular film can be made, or manually adjust the color balance during the printing operation. These operations are undesirable, leading to higher operating costs, decreased printer output and increased chance of operator error.
U.S. application Ser. No. 08/075,068 filed Jun. 10, 1993, describes the use of photographically inert colorants with peak absorbance of 560-590 nm to improve the printer compatibility between multilayer films that contain magenta image dyes with low absorbance between 560-590 nm compared to film containing other types of magenta dyes. However, this method is limited because the correction is not imagewise. The amount of density between 560-590 nm provided by the inert dye is fixed and constant throughout the exposure scale. At high exposures (high amounts of magenta dye), the amount of correction will be insufficient, whereas at low exposures (low amounts of magenta dye), the correction will be excessive. Only at one point in the exposure scale will the degree of correction be ideal.
EP 0 529 784 A1 describes the combination of a 4-phenylazo-1-pentachlorophenyl-3-anilino-5-pyrazolone masking coupler with photographically inert dyes having peak absorbance of 590-610 nm to improve printer compatibility. As indicated, the degree of hue correction from the inert dye will be non-linear. 1-Pentachlorophenyl-3-anilino-5-pyrazolone masking couplers produce a bathochromic dye relative to analogous 1-trichlorophenyl-3-anilino-5-pyrazolones that are typically used as magenta image couplers, but are still insufficiently bathochromic to produce enough density in the 565-600 nm region to provide the degree of correction necessary.
It would be desirable to have color negative films containing 1-phenyl-3-anilino-5-pyrazolone magenta couplers or other couplers which produce a magenta image dye with low density in the 565 to 600 nm range, which can be printed in the various available printers without segregating them from other films or manually adjusting color balance, and still obtain paper prints with good color balance.